Machupo virus (MV; Arenaviridae: Tacaribe VComplex; Machupo) is the etiologic agent for Bolivian Hemorrhagic Fever (BHF). MV is a rodent- borne, segmented, negative-sense RNA virus that shares many replicative, pathophysiologic, and epidemiologic features with the genus Hantavirus, family Bunyaviridae. As with hantaviruses, each arenavirus species except one is harbored by a specific rodent host in the family Muridae. Less is known about the specifics and geographic feature of these viral/host associations than for those of the hantaviruses and their hosts. This project will evaluate the relationship between prevalence of Machupo virus infection in wild populations of Bolivian rodents in relation to human land use patterns and rodent ecology. Using previously collected specimens, we will examine rodents of the murid subfamily Sigmodontinae from throughout Bolivia for seroprevalence of Machupo virus antibodies and evaluate any variation in levels of infection in light of differences in rodent abundance and difference in habitat. Viruses and rodent reservoir species will be characterized using cytogenetic and molecular genetic techniques. Specifically, we propose to test the following hypotheses; 1) The distribution of human cases of BHF is a function of habitat type and not geographic distribution of the reservoir species, 2) Human land-use patterns including habitat disturbance in northern Bolivia favors increased abundance of MV reservoir species and thus increases the risk of human disease the risk of human disease, and 3) levels of rodent abundance are positively correlated with seroprevalence of MV (e.g., as rodent populations increase in density, the percentage of the population infected with MV increases). These data will greatly expand our knowledge of MV and our understanding of Arenaviruses in general.